The invention concerns apparatus for weighing granular or pulverulent bulk goods, wherein the bulk goods are moved by reduced pressure from a silo through at least one conveyance duct to a scale, the flow of material being lessened toward the end of the conveyance procedure by increasing the proportion of air in order to properly meter the process.
In known equipment of this kind, an air feeding branch line is connected to the conveyance duct with the shutoff valve of the branch line being opened near the end of the weighing procedure so that additional air enters the conveyance duct to lower the flow of material. In this manner the material conveyed per unt time is decreased and it is easier to carry out a metering process at the end of the weighing procedure.
This known equipment incurs the drawback that the uniformity of the flow of material is degraded by the supply of additional air, whereby the flow of material enters the scale with varying densities. The reduced-pressure conveyance furthermore may cause at least part of the material to accumulate in front of the branch pipe when the additional air is applied, whereby at times there is no conveyance of material at all.